1. Field of the Invention
The present invention has as its object a method for the selective dissolution of lead, in the presence of zinc in the form of a sulphurized compound.
It is concerned more particularly with a technique that makes it possible to prepare zinc concentrates that contain very little lead from lead-zinc concentrates.
2. Description of the Prior Art
During the last few decades, the classical minerals of blende and galena have been exhausted, and the new deposits which have been discovered are essentially micro-crystallized deposits of mixed minerals, the components of which are difficult to separate by the conventional techniques of differential flotation.
The mining industry currently finds itself confronted with two alternatives. The first possibility consists of performing a flotation separation. Flotation separation is expensive in terms of energy consumption, since these flotations require an extremely fine crushing process on the order of 10 micrometers. Additionally, flotation separation produces very low yields, in some cases less than 50%. The second possibility consists of obtaining mixed lead-zinc concentrates, the market value of which is low, inasmuch as those mixed concentrates cannot be processed in all zinc works, a fact that entails considerable commercial penalties.
Prior to the present invention, it has already been proposed, particularly in the French Patent Application filed by the Applicant and published under the number 2,359,221, that the lead be dissolved with the aid of cupric chloride.
No matter what interest that technique may have, it had, and still has, the serious disadvantage that the concentrate of zinc obtained in that manner is contaminated with considerable quantities of copper. That has a two-fold disadvantage; in the first place, the loss of copper represents an unnecessary expense; and, in the second place, the zinc concentrate that is produced has diminished value in the marketplace because of the high percentage of copper that is present as an impurity.
The teaching of the above patent with slight variants has been confirmed by the Disburger Kupferhutte U.S. Pat. No. 4,260,588 and by Hazen Research Inc. U.S. Pat. No. 4,276,084. However, each of those variants have the same disadvantages as described in the preceding paragraph. Thus, a need has continued to exist for a method that makes it possible to produce a zinc concentrate uncontaminated with copper.